WO2011064762A1

WO2011064762A1 - Production of a fermented foodstuff

Info

Publication number: WO2011064762A1
Application number: PCT/IB2010/055496
Authority: WO
Inventors: Jacobus Myburgh; Esti-Andrine Smith
Original assignee: University Of The Free State
Priority date: 2009-11-30
Filing date: 2010-11-30
Publication date: 2011-06-03
Also published as: ZA201201139B

Abstract

This invention relates to a method of producing a fermented foodstuff including the steps of providing a primary growth medium; providing a microorganism starter culture in the pre-incubation phase; inoculating the primary growth medium with the starter culture; allowing the starter culture to proliferate to the linear growth phase to form an inoculant; providing a secondary bulk growth medium; inoculating the secondary bulk growth medium with the inoculant whilst in the linear growth phase; and allowing the inoculant to proliferate to ferment the secondary bulk medium into the fermented foodstuff. The applicant has found that the method according to the invention reduces the production time of yogurt with at least 20%.

Description

TITLE: PRODUCTION OF A FERMENTED FOODSTUFF

INTRODUCTION AND BACKGROUND

This invention relates to a method of producing a fermented foodstuff. More particularly, this invention relates to the production of fermented dairy products.

It has long been known that yogurt and other fermented dairy foodstuffs could be produced by adding a starter culture directly to milk. Typically, yogurt has been produced by inoculating milk with different cultures such as Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus salivarius subsp. thermophilus as starter culture, in dried or freeze-dried form. The starter culture ferments lactose in the milk into lactic acid and lowers the pH of the milk.

A disadvantage of known methods of producing fermented foodstuffs is that the starter culture is added in a dried, frozen or freeze-dried form, whilst still in the pre-incubation phase, causing a delay in the manufacturing process, owing to the fact that the starter culture first has to proliferate into the linear growth phase before the foodstuff is fermented at an acceptable rate. When manufacturing yogurt, this could cause a substantial delay in the manufacturing process. This increases the manufacturing time and thus the cost of the fermented end product. There is therefore a commercial need for reducing fermentation period in preparing a foodstuff.

OBJECT OF THE INVENTION

It is accordingly an object of the present invention to provide a method with which the aforesaid disadvantage could be overcome or at least minimised. It is another object of the invention to provide a method for reducing the fermentation period in producing a foodstuff.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a method for producing a fermented foodstuff including the steps of:

- providing a primary growth medium;

- providing a microorganism starter culture in the pre-incubation phase;

- inoculating the primary growth medium with the starter culture;

- allowing the starter culture to proliferate to the linear growth phase to form an inoculant;

- providing a secondary bulk growth medium;

- inoculating the secondary bulk growth medium with the inoculant whilst in the linear growth phase; and - allowing the inoculant to proliferate to ferment the secondary bulk medium into the fermented foodstuff.

The primary growth medium may be selected from the group consisting of milk, milk powder, and various fractions of milk, including whey, cream and the like.

In the case where the primary growth medium is in the form of milk powder, the step of providing the primary growth medium may include the further step of hydrating the milk powder from 2% to 20%, preferably 10% on a mass per volume (w/v) basis.

The step of providing the primary growth medium may include the further step of removing most of the casein protein from the milk.

The steps of removing the casein protein may include the step of denaturing some of the whey protein in the milk and allowing some of the denatured whey protein to adhere to some of the casein protein, forming a protein complex.

The step of denaturing the casein protein may include the step of increasing the temperature of the milk to a temperature between 50 degrees Celsius and 150 degrees Celsius, preferably 90 degrees Celsius. The step of removing the casein protein may include the further step of destabilising the protein complex, by cooling the milk to ambient temperature; and by adjusting the pH of the milk to between pH 3 and pH 8, preferably pH 4.6.

The step of removing the casein protein may include the further step of removing a substantial fraction of the casein and the protein complex from the milk, by centrifuging the milk; and adjusting the pH of the milk to between pH 3 and pH 8, preferably pH 6.5.

The step of removing the casein protein may include the further steps of elevating the temperature of the milk to a temperature of between 20 degrees Celsius and 80 degrees Celsius, preferably 42 degrees Celsius; thus denaturing residual casein protein; and centrifuging of the milk to remove the residual denatured casein protein to form a clear serum or primary growth medium.

Further according to the invention, the microorganism starter culture is selected from the group consisting of bacterial species, fungal species and more specific yeast species. The microorganism starter culture may be selected from the group consisting of Lactococcus species, Streptococcus species, Enterococcus species, Erwinia species, Leuconostoc species, Pediococcus soecies. Bifidobacterium species, Lactobacillus species and Micrococcus species, preferably Streptococcus salivarius spp. thermophilus and Lactobacillus delbrueckii subsp. Bulgaricus and combinations thereof. Preferably, the microorganism starter culture contains an equal ratio of Streptococcus salivarius spp. thermophilus and Lactobacillus delbrueckii subsp. bulgaricus.

According to a second aspect of the invention there is provided a foodstuff prepared by a method according to the first aspect of the invention.

The fermented foodstuff may be selected from the group consisting of yogurt, buttermilk, maas, kefir, kumis, and cheese. According to a third aspect of the invention there is provided a proliferation apparatus for preparing an inoculant in the linear growth phase for use in a method according to the first aspect of the invention, the proliferation apparatus comprising a body defining a first chamber for containing a primary growth medium prepared in accordance with said method; a second chamber for containing a microorganism starter culture in the preincubation phase; and separating means for separating the first and second chambers, the separating means being openable to connect the insides of the chambers to each other to inoculate the primary growth medium with the microorganism starter culture, to allow proliferation of the said microorganism to the linear growth phase to form the said inoculant.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described further, by way of example only, with reference to the accompanying drawings wherein: figure 1 is a graph depicting the growth curve (optical density at 640 nm) of a microorganism starter culture in a primary growth medium for use in a method according to a preferred embodiment of the invention; figure 2 depicts the fermentation time of a foodstuff prepared in accordance with a method of the present invention in comparison with the fermentation time of a foodstuff prepared with a prior art method using a microorganism starter culture in the pre-incubation stage; and figure 3 is a representation of a proliferation apparatus according to a preferred embodiment of a third aspect of the invention. DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

According to a preferred embodiment of the invention there is provided a method for producing a fermented foodstuff including the steps of:

- providing a primary growth medium;

- providing a microorganism starter culture in the pre-incubation phase;

- inoculating the primary growth medium with the starter culture;

- providing a secondary bulk growth medium;

- inoculating the secondary bulk growth medium with the inoculant whilst in the linear growth phase; and

- allowing the inoculant to proliferate to ferment the secondary bulk medium into the fermented foodstuff.

Further details of respective steps in the method according to the invention:

Preparation of primary growth medium substantially free of casein The first step of the method, according to a preferred embodiment of the invention, is to provide a primary growth medium substantially free of casein. In the preparation of the primary growth medium, skim milk powder is hydrated to 10% (w/v) total solids whilst elevating the temperature thereof to 50 degrees Celsius for at least 60 minutes, in a 500ml Erlenmeyer flask with a cotton wool plug.

Subsequently, the temperature of the hydrated milk is elevated to 90 degrees Celsius for a period of 40 minutes, to initiate pasteurisation and to provide sufficient time for partial denaturing of some of the whey protein in the milk. Some of the denatured whey protein is allowed to adhere to the casein protein in the milk, forming a protein complex. The milk is then cooled to ambient temperature (±25 degrees Celsius).

The pH of the milk is adjusted with 36% hydrochloric acid (Merck, analytical grade) to pH 4.6, the iso-electric point of casein, to destabilise the casein protein as well as the whey/casein protein complex. The milk is centrifuged for 5 minutes, at 9820 g (Beckman Model J2-21 centrifuge) resulting in the casein and said protein complex to precipitate in a whitish precipitate, with a yellow supernatant (serum) remaining.

The pH of the serum is adjusted to pH 6.5, with 0N sodium hydroxide (Saarchem, analytical grade). The temperature of the serum is subsequently elevated to 42 degrees Celsius for 30 minutes to denature any residual casein protein. The serum is then centrifuged for 5 minutes, at 9820 g to remove any residual denatured casein protein from the serum, thus to form a clear primary growth medium. The primary growth medium is stored for 5 hours (overnight) at 4 degrees Celsius. Preparation of inoculant

According to a further step of the invention, the prepared primary growth medium is inoculated with a microorganism starter culture in the preincubation phase. The starter culture is selected from the group consisting of bacterial species, fungal species and more specifically yeast species. In the case of bacterial species, the microorganism starter culture is selected from the group of lactic acid bacterial species comprising Lactococcus species, Enterococcus species, Erwinia species, Leuconostoc species, Pediococcus species, Bifidobacterium species, Micrococcus species, Streptococcus species, and Lactobacillus species and combinations thereof.

In accordance with the preferred embodiment of the method of the invention, Streptococcus salivarius spp. thermophilus and Lactobacillus delbrueckii subsp. bulgaricus, (for example: FD-DVS YF-L812 Yo-Flex, supplied by Chr. Hansen), in freeze dried format, are used. The freeze- dried starter culture granules are ground to ensure uniformity and equal distribution and an equal ratio of the two aforesaid starter culture microorganisms. The temperature of the primary growth medium (300 ml) is adjusted to 42 degrees Celsius and then inoculated with 0.1g of an equally distributed active form of the microorganism starter culture in the pre-incubation phase. The microorganism starter culture is allowed to proliferate in the primary growth medium to form an inoculant in the linear growth phase.

The growth of the starter culture in the primary growth medium is monitored at 640 nm at hourly intervals for 8 hours (figure 1 ), during incubation at 42 degrees Celsius in a shaker, at 100 rpm, to determine the number of hours that it would take for the starter culture to reach the linear growth phase and specifically the optimum linear growth phase and at which the secondary bulk growth medium is preferably to be inoculated with the inoculant. After each hour of growth, a separate batch of secondary growth medium was inoculated with the inoculant. Each batch was monitored for eight hours at 15 minutes intervals until the secondary bulk medium was fully fermented to yogurt i.e. the yogurt was set and had a pH of 4.6. In figure 2, the set time of yogurt prepared using a starter culture in the pre-incubation stage, similar to the prior art, is compared to the batch which had the shortest set time.

It was found that when the inoculant, which proliferated in the primary growth medium for 3 hours, prior to being inoculated into the secondary bulk growth medium, was in the linear growth phase. It was further surprisingly found that this inoculant set the yogurt 20% faster than when using a starter culture in the pre-incubation stage as is done in the prior art, as is evident from figure 2.

Inoculation of secondary bulk growth medium with an inoculant

Therefore, in accordance with a further step of the invention, the secondary growth bulk medium, in the form of milk, is inoculated with the inoculant whilst the starter culture is in the linear growth phase. The inoculant is allowed to proliferate and to ferment the milk into yogurt in conventional fashion, the difference being that the end point is achieved in at least 20% shorter time than with prior art methods.

The applicant has further surprisingly found that grinding of the microorganism starter culture before inoculation to the primary growth medium results into reproducibility between the individual production batches of the starter culture.

Referring to figure 3, applicant foresees that, for commercial application of the invention, a proliferation apparatus 10 according to a third aspect of the invention could be provided. The proliferation apparatus 10 comprises a body 1 1 , defining a first chamber 12 containing the said primary growth medium 14; and a second chamber 16 containing the said microorganism starter culture 18. The starter culture 18 is in freeze dried form in the preincubation stage and is ground prior to being introduced to the chamber 16. The first and second chambers 12 and 16 are separated from one another by an openable separating seal 20. The separating seal 20 is openable to connect the insides of the chambers 12 and 16 to each other to inoculate the primary growth medium 14 with the starter culture 18, to allow activation and proliferation of the said starter culture 18 from the pre- incubation stage to the linear growth phase. The separating means 20 and insides of the chambers 12 and 16 are rendered sterile prior to the apparatus being filled with the growth medium 14 and starter culture 18.

The separating seal 20 is a connecting strip, which connects the two chambers 12 and 16 together. The integrity of the separating strip 20 is relatively less than the outer walls of the proliferation apparatus 10, such that, when pressure is applied to the proliferation apparatus 10, the integrity of the separating seal 20 is compromised to connect the insides of the chambers 12 and 16, without the integrity of the outer wall being compromised.

The primary growth medium chamber 12 has a first port 24 and the microorganism starter culture chamber 16 has a second port 26. The ports 24 and 26 are integrally formed with the chambers 12 and 16 respectively. Each port 24 and 26 includes a quick connect coupling 28 for anaerobically sealing the ports 24 and 26 and thus also the chambers 12 and 16.

The ports 24 and 26 and coupling 28 are adapted to allow filling of the respective chambers 12 and 16 with the primary growth medium 14 and culture 18. It will be appreciated that for freeze dried culture 18, a relatively larger port 26 would have to be employed when filling the chamber 16.

The proliferation apparatus 10 is made of a flexible multilayer film 22, having at least three layers. The outer and inner layers are a polymeric material and the middle layer, which is sandwiched between the outer and inner layers, is a metallic foil layer.

The proliferation apparatus 10 is further provided with a closable dispensing port 30 towards the bottom thereof. The dispensing port 30 is also provided with a quick connect coupling 29, being the same as the coupling 28. The proliferation apparatus 10 further includes a suspending formation 32, in the form of an opening for allowing the proliferation apparatus 10 to be suspended. In use, the temperature of the primary growth medium 14 is elevated to 42 degrees Celsius; the seal 20 opened, and the starter culture 18 mixed with the growth medium 14 and allowed to proliferate to form an inoculant in the linear growth phase. The bulk growth medium (not shown) is inoculated with the inoculant in accordance with the method of the invention.

It will be appreciated that many other configurations of the proliferation apparatus 10 could, of course, be used. It will be appreciated further that variations in detail are possible with a method of producing a fermented foodstuff according to the invention without departing from the scope of the appended claims.

Claims

1. A method for producing a fermented foodstuff including the steps of providing a primary growth medium; providing a microorganism starter culture in the pre-incubation phase; inoculating the primary growth medium with the starter culture; allowing the starter culture to proliferate to the linear growth phase to form an inoculant; providing a secondary bulk growth medium; inoculating the secondary bulk growth medium with the inoculant whilst in the linear growth phase; and allowing the inoculant to proliferate to ferment the secondary bulk medium into the fermented foodstuff.

2. A method according to claim 1 wherein the primary growth medium is selected from the group consisting of milk, milk powder, and various fractions of milk, including whey and cream.

3. A method according to claim 2 wherein the primary growth medium is milk powder and wherein the step of providing the primary growth medium includes the further step of hydrating the milk powder from 2% to 20%, preferably 10% on a mass per volume (w/v) basis to form milk and wherein the method includes the further step of removing a majority portion of the casein protein from the milk. A method according to claim 3 wherein the step of removing the majority portion of the casein protein includes the further step of denaturing some of the whey protein in the milk and allowing some of the denatured whey protein to adhere to some of the casein protein, forming a protein complex.

A method according to claim 4 wherein the step of removing the majority portion of the casein protein includes the further step of increasing the temperature of the milk to a temperature of between 50 and 150 degrees Celsius, preferably 90 degrees Celsius.

A method according to claim 5 wherein the step of removing the majority portion of the casein protein includes the further step of destabilising the protein complex by cooling the milk to ambient temperature; and by adjusting the pH of the milk to between pH 3 and pH 8, preferably pH 4.6.

A method according to claim 6 including the further step of removing a substantial fraction of the casein and the protein complex from the milk, by centrifuging the milk; and adjusting the pH of the milk to between pH 3 and pH 8, preferably pH 6.5. A method according to claim 7 including the further steps of elevating the temperature of the milk to a temperature of between 20 and 80 degrees Celsius, preferably 42 degrees Celsius, thus denaturing residual casein protein; and centrifuging the milk to remove the residual denatured casein protein to form a clear serum providing a primary growth medium.

A method according to any one of claims 1 to 8 wherein the microorganism starter culture is selected from the group consisting of bacterial species, fungal species and yeast species.

A method according to claim 9 wherein the microorganism starter culture is selected from the group consisting of Lactococcus species, Streptococcus species, Enterococcus species, Erwinia species, Leuconostoc species, Pediococcus species, Bifidobacterium species, Lactobacillus species and Micrococcus species, preferably Streptococcus saliva us spp. thermophilus and Lactobacillus delbrueckii subsp. Bulgaricus and combinations thereof. A method according to claim 10 wherein the microorganism starter culture contains an equal ratio of Streptococcus saliva us spp. thermophilus and Lactobacillus delbrueckii subsp. bulgaricus. A fermented foodstuff prepared according to a method of any one of claims 1 to 1 1 wherein the fermented foodstuff is selected from the group consisting of yogurt, buttermilk, maas, kefir, kumis, and cheese.

A proliferation apparatus for preparing an inoculant in the linear growth phase for use in a method according to any one of claims 1 to 12 wherein the proliferation apparatus comprising a body defining a first chamber for containing a primary growth medium prepared in accordance with said method; a second chamber for containing a microorganism starter culture in the pre-incubation phase; and separating means for separating the first and second chambers, the separating means being openable to connect the insides of the chambers to each other to inoculate the primary growth medium with the microorganism starter culture, to allow proliferation of the said microorganism to the linear growth phase to form the said inoculant.

A method for producing a fermented foodstuff substantially as herein described and exemplified.

15. A proliferation apparatus for preparing an inoculant in the linear growth phase substantially as herein described a with reference to figure 3.